The present invention relates generally to hot water dispensing systems having a plastic heating tank. In particular, the present invention relates to a water heating tank with a float switch sensor and thermal cutout devices for protecting the tank when the tank has little or no water.
Hot water dispensers are known in the marketplace. As used herein, xe2x80x9chot waterxe2x80x9d refers to water at temperatures at or about 190xc2x0 Fahrenheit (88xc2x0 Celsius), but at or below the boiling point of water (212xc2x0 Fahrenheit/100xc2x0 Celsius). Water at this high temperature can be made available at a dedicated faucet for users needing hot water to make, for example, coffee, tea, or cocoa. A typical dispenser heats water in a relatively small tank that is situated below the sink on which the dedicated faucet is mounted. The tank may have a capacity of ⅓ or xc2xd gallon (1.3 or 1.9 liters). The tanks are usually divided into multiple chambers, such as a main chamber and an expansion chamber. Water is heated electrically by a heating element in the main chamber. The expansion chamber is contiguous with the main chamber and contains water that is initially heated in the main chamber and allowed to expand into the expansion chamber to preclude pressure buildup generated by heating the water.
Most known water heating chambers and tanks utilize metal fabricating wherein several pieces of metal must be integrated together to create separate air and watertight chambers. The fabrication of metal tanks is labor intensive and requires expensive cleaning operations. Metal tanks are also susceptible to leaks because the tank is made from several pieces of metal.
As a result, a hot water dispenser with a plastic tank was developed and is the subject of application Ser. Nos. 09/396,387 and 09/026,070, which are owned by the assignee and incorporated herein by reference in their entirety. As explained in those applications, the plastic tank is cheaper and easier to fabricate. The plastic tank, however, is vulnerable to damage when the heating element is activated when little or no water is present in the tank. For instance, damage is likely to occur during an accidental xe2x80x9cdry start,xe2x80x9d which happens after installation of the tank and before water has been introduced into the system. Hot water dispensers are typically not sold with an on/off switch, so once the unit is plugged in, the heater will be energized. Damage may also occur during a rare xe2x80x9cboil dryxe2x80x9d condition, when the water in the tank boils until the water level becomes too low. Damage to a tank may occur very quickly, within the first minute or two after the heating element is energized. By the time a person or system recognizes the problem, it is typically too late to avoid damage.
Accordingly, a need exists to prevent damage to a tank when little or no water is present in the tank. Application Ser. No. 09/479,190, which is owned by the assignee and incorporated herein by reference in its entirety, discloses a tank for a hot water dispenser that includes at least one heat dissipation plate. Heat is diverted from the walls of the tank to the heat dissipation plate. The present invention, however, prevents damage to the tank by inhibiting the activation of the heating element when little or no water exists in the tank. By inhibiting the heating element from energizing, the potential for excessive heat generation is eliminated.
To that end, the present invention provides a heating tank assembly for a hot water dispenser having a tank body, an electric heating element, a magnetic switch, and a movable float. The tank body has a plurality of walls and a main heating chamber for storing and heating water. At least a portion of the electric heating element is located within the main heating chamber of the tank body. The magnetic switch is electrically connected to the heating element and acts as a protective switch to the heating element. The movable float is located within the tank body and has a magnet that closes the magnetic switch when sufficient water is present in the tank.
The tank body and movable float are preferably made of molded plastic. The float may, alternatively, be made of plastic with a foaming agent. The magnetic switch is preferably a Reed switch. In one embodiment, the magnetic switch is normally open. As sufficient water is added to the heating tank assembly, the float moves within proximity to the magnetic switch and closes the switch, enabling the heating element to be energized. The magnetic switch, however, may also be normally closed. In this embodiment, the float is already in close proximity to the switch when little or no water is present in the tank. As sufficient water is added to the heating tank assembly, the float moves away from the magnetic switch and closes the switch, enabling the heating element to be energized.
The heating tank assembly may also include at least one thermal cutout device. The thermal cutout device is located in close proximity to a portion of the heating element that is outside the tank body. The thermal cutout device acts as a thermal fuse and can shut off the heating element when the heating element reflects a preset temperature.
In another embodiment, the present invention provides a hot water dispenser having a plastic molded tank body, an electric heating element, and a switch. The plastic molded tank body has a plurality of walls and a main heating chamber for storing and heating water. The heating element extends at least partially into the heating chamber through a bushing mounted to a hole in the tank body. The switch is electrically connected to the heating element and is capable of determining whether little or no water is present in the tank body. The switch inhibits the activation of the heating element if the tank body has little or no water.
In a further embodiment, the present invention is a method for determining whether a heating tank assembly of a hot water dispenser has little or no water. The method includes providing a unitary plastic molded tank body, an electric heating element, a magnetic switch, and a movable float. The tank body has a heating chamber, and at least a part of the heating element is located within the heating chamber. The magnetic switch is electrically connected to the heating element. The movable float is located within the tank body and has a magnet. The method includes the steps of moving the float within proximity to the magnetic switch and closing the magnetic switch when sufficient water is present in the tank body. In another embodiment, the method includes the alternative steps of moving the float away from the magnetic switch and closing the magnetic switch when sufficient water is present in the tank body.
In yet another embodiment, the present invention is a method for manufacturing a heating tank assembly of a hot water dispenser. The method includes the steps of providing a unitary molded plastic tank body having a heating chamber, providing an electric heating element, mounting the electric heating element to the tank body, providing a magnetic switch, mounting the magnetic switch to the tank body, electrically connecting the magnetic switch to the heating element, providing a float that has a magnet, and positioning the float in the tank body such that the magnet of the float closes the magnetic switch when sufficient water is present in the tank body.
In another embodiment, a heating tank assembly is provided and includes a tank body, an electric heating element, and at least one thermal cutout device. The tank body has a plurality of walls and a main heating chamber for storing and heating water. The heating element is mounted to the tank body and has a first portion located outside the tank body and a second portion located inside the tank body. The thermal cutout device is located in close proximity to the first portion of the heating element and is capable of shutting off the heating element when the heating element reaches a preset temperature. The thermal cutout device may also be wrapped in insulating tape to prevent shorting to the heating element.